Background:  The identification of new broadly cross-reactive HIV neutralizing human monoclonal antibodies and characterization of their conserved epitopes is important for the development of HIV inhibitors and vaccines. Only 3 such antibodies to gp41 of the HIV-1 envelope glycoprotein have been identified and characterized—2F5, 4E10, and Z13. To select antibodies against gp41 in the context of an Env that is close to the native conformation, but purified, we used soluble recombinant Env (gp140s) from several primary isolates and developed a method termed competitive antigen panning (CAP) that enhances the selection of antibodies against gp41 relative to those against gp120.

Methods:  We used an immune antibody library constructed from the bone marrow of 3 HIV-1-infected long-term nonprogressors and CAP, where labeled gp140 is mixed with excess of unlabeled gp120 and used for panning of the library.

Results:  We selected 6 anti-gp41 Fabs, designated m43-48. They bound gp140 but not gp120 from primary isolates with high affinity and neutralized HIV-1 primary isolates to various extents in 2 cell-free virus neutralization assays based on infection of PBMC and pseudovirus. These anti-gp41 antibodies bound to 6-helix bundles of gp41 and peptides from the membrane proximal region. Some of them competed with Z13 and 2F5 but others did not; however, all competed with T3 that binds to a 15-mer peptide comprising the very C-terminal region of the gp41 ectodomain. The characterization of their neutralizing activity and epitopes continues, and the results will be reported at the conference.

Conclusions:  These results suggest that new cross-reactive anti-gp41 HIV-1-neutralizing human monoclonal antibodies can be identified by using new methods, and that such antibodies are likely to exist in infected individuals. These antibodies may have potential as therapeutics in combination with other antibodies and antiretroviral drugs, and the identification and characterization of their epitopes could help in the development of vaccine immunogen that can elicit them in vivo.

Keywords: entry inhibitors; neutralization antibodies; fusion protein